As printing plate technology has steadily evolved in recent years from analog imaging materials and methods to digital imaging materials and methods, a number of imaging techniques capable of use in digital printing have been described for use in computer-to-plate imaging systems. Examples of these digital printing technologies for computer-to-plate applications include laser printing, laser-induced thermal ablation imaging, and ink jet printing.
Throughout this application, various publications, patents, and published patent applications are referred to by an identifying citation. The disclosures of the publications, patents, and published patent applications referenced in this application are hereby incorporated by reference into the present disclosure to more fully describe the state of the art to which this invention pertains.
Exemplary of laser printing techniques for computer-to-plate applications is U.S. Pat. No. 5,304,443 to Figov. Examples of laser-induced thermal ablation techniques for computer-to-plate applications include U.S. Pat. Nos. 5,353,705 and 5,487,338, both to Lewis et al., and U.S. Pat. Nos. 5,605,780 and 5,691,114, both to Burberry, et al. U.S. Pat. No. 4,003,312 to Gunther, U.S. Pat. No. 4,833,486 to Zerillo, U.S. Pat. No. 5,312,654 to Arimatsu et al., U.S. Pat. No. 5,501,150 to Leenders et al., U.S. Pat. No. 5,738,013 to Kellett, Japanese Kokai 62-25081 to Katagiri et al., and EP 776,763A1 to Hallman et al. are examples of ink jet printing techniques for computer-to-plate applications.
Lithographic printing has long been a widely used printing technique. The term "lithographic," as used herein, is meant to include various terms used synonymously, such as offset, offset lithographic, planographic, and others. Much effort has been directed at developing computer-to-plate imaging techniques for providing lithographic printing plates. These efforts have been made for both of the main types of lithographic printing plates: wet lithographic printing plates and dry or waterless printing plates.
By the term "wet lithographic," as used herein, is meant the type of lithographic printing plate where the inking or image areas of the plate that receive the printing ink from the ink roller and then transfer this ink to the receiving media, such as a type of paper, are ink-receptive or oleophilic and where the non-inking or background areas of the plate that do not accept printing ink from the ink roller and thus do not transfer any ink to the receiving media are hydrophilic and receive an aqueous fountain solution during the printing process before contact with the ink roller. This aqueous or "wet" layer in the non-inking areas renders these areas ink repellent or oleophobic to the printing ink.
By the terms "dry lithographic" or "waterless lithographic," as used herein, is meant the type of lithographic printing plate where the inking or image areas of the plate that receive the printing ink from the ink roller and then transfer this ink to the receiving media are ink-receptive and where the non-inking or background areas of the plate that do not accept printing ink from the ink roller and thus do not transfer any ink to the receiving media are ink-releasing in a "dry" or "waterless" state and do not utilize a "wet" solution of any type, such as an aqueous fountain or dampening solution, to render the non-inking areas repellent to the printing ink. Thus, the dry or waterless lithographic printing process has an advantage over the wet lithographic printing process in that the operator does not have the additional variable of an aqueous fountain solution to identify as suitable for the specific printing operation and then to have to maintain throughout the course of the printing operation. This advantage from simpler equipment, processing, and printing solution and other setup requirements is particularly useful in computer-to-plate lithographic printing where a fast setup and turnaround time for the printing run is highly desirable to achieve the overall printing speed and convenience possible from computer-to-plate based printing systems.
For waterless lithographic printing, the ink-releasing material in the non-inking areas of the plate is typically a material of low surface energy, such as a surface tension below about 20 dynes/cm, which makes the layer abhesive or repellent to the oil-based waterless printing inks as well as to aqueous dampening solutions. To provide this low surface energy, elastomeric silicone polymer materials are commonly used for waterless lithographic printing plates, as for example, described in U.S. Pat. No. 4,259,905 to Abiko et al., U.S. Pat. No. 5,017,457 to Herrman et al, and U.S. Pat. No. 5,212,048 to Lewis et al. Computer-to-plate printing for use in waterless lithographic printing is known, as, for example, described in U.S. Pat. Nos. 5,310,869, 5,339,737, 5,540,150, and 5,551,341, all to Lewis et al., for laser-induced thermal ablation and in U.S. Pat. No. 4,003,312 for ink jet printing. Some disadvantages of silicone materials for waterless lithographic plates include poor adhesion of the silicone-containing layer to support materials, such as aluminum plates, and soft and elastomeric properties which may interfere with the durability needed for long press runs, such as over 50,000 impressions, and which may not cleanly release the elastomeric and somewhat tacky waterless printing inks to provide high resolution and consistent image quality. To overcome the intrinsic abhesive properties of the silicone materials, one or more additional layers have been utilized to improve the adhesion to the support material. Thus, it would be desirable to have a tough, durable material with good adhesion to the support material and with excellent ink-releasing properties for use in various computer-to-plate systems to prepare waterless lithographic plates, particularly those capable of long production runs of 50,000 impressions and more with a consistent image quality.
As an alternative to silicone materials as the low surface energy materials for the ink-releasing areas in waterless lithographic plates, fluorinated materials have been reported, such as, for example, U.S. Pat. No. 3,859,090 to Yoerger et al., which describes a fluorinated acrylate polymer with a fluorinated or silicone oil in an ink repellent composition for waterless plates.
An ink-releasing material, which is applicable for waterless lithographic printing plates and provides a tough, durable layer with excellent ink-releasing properties, and which may be utilized in computer-to-plate imaging processes, such as laser-induced thermal ablation and ink jet printing, would be of great value to the printing industry.